Sony's latest PS3 firmware upgrade (2.52) has resulted in a small but significant minority of machines (including mine) suddenly being unable to play discs. At all. That's right, no games, no DVDs, no Blu-Ray. Can still play anything on the hard drive, but that's a very small proportion of what we use it for.
Looking at the forums, Sony are being completely unsympathetic about it. I will be expecting a lot better when I call tomorrow.
Thankfully, my machine is still in warranty (just), but it does seem a bit much that if Sony break it after the warranty elapses, they are somehow not liable. And yet you can't choose not to upgrade (well you can, but then you can't do anything online).